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| High-voltage continuous miner |
Description of Problem
The demand for larger, more powerful mining equipment stimulated the need for increased voltages for coal mine face machinery. Higher-voltage equipment can supply more power without the need for larger, heavier trailing cables. Special design, use, and maintenance precautions are needed to ensure an equivalent level of safety when high-voltage systems are used in permissible areas. The voltage limit for type-accepted continuous miners is 1,000 V ac. Equipment operating above 1,000 V ac requires a petition for modification. This entails an approval examination for each high-voltage continuous miner deployed inby.
Research and Development Activities
NIOSH conducted research studies indicating that higher voltages for face equipment was feasible with appropriate precautions. In addition to the studies used to develop the high-voltage longwall final rule, Information Circular (IC) 9258, "Mine Power Systems," provided information used to specify important shock protection sections of the continuous miner proposed rule.
R&D Outputs and Transfer Activities
Results drawn from at least five separate NIOSH reports were used to help formulate the technical language in the proposed rule. These studies provided critical parts of the technical basis for the proposed MSHA regulations. The information used from the reports included the enclosure pressures developed during electrical arcing at up to 15 kV in methane-air atmospheres. Also included were recommendations for high-voltage electrical creepage and clearance distances, design criteria for explosion-proof enclosures, permissibility hazard reduction, and ground fault protection. MSHA used these reports in rulemaking regarding Part 6 equivalency determinations for Part 18 enclosures. MSHA also used them to help reconcile philosophical differences in other standards (both foreign and domestic) for designing explosion-proof enclosures.
Description of Intermediate Outcome
MSHA has proposed new requirements (Federal Register, July 16, 2004, Vol. 69, No. 136, proposed rules, pp. 42811-42840) for the approval of high-voltage continuous mining machines operating in face areas of underground mines: http://www.msha.gov/REGS/FEDREG/PROPOSED/2004prop/04-15841.pdf. The proposed rule was published to allow type acceptance of continuous mining machines, thus avoiding the petition for modification process for each high-voltage continuous miner placed into service. MSHA also proposed new mandatory electrical safety standards for the installation, use, and maintenance of high-voltage continuous mining machines used in underground coal mines. These provisions will enable mines to use type-accepted high-voltage continuous mining machines with enhanced safety protection from fire, explosion, and shock hazards.